Rapid prototyping systems are now under development in an attempt to provide single automated systems which can produce prototypes and small production runs directly from engineering drawings. There are currently several types of such systems, some of which types are described in the background section of U.S. Pat. No. 5,398,193 of deAngelis, which section is incorporated herein by reference thereto.
As discussed in the referenced patent, the typical system includes a source of material, a material deposition system such as a nozzle, a material receiving platform, and means for moving the platform in at least three directions with respect to the deposition system under the control of a computer. The material typically flows through the nozzle as either a powder or a liquid and is hardened by some process when it hits the platform or a previous hardened layer of material. Objects are formed by spraying and hardening successive slices of the final object.
For systems based on depositing a colloidal slurry, the ideal system would permit a rapid flow of material from the nozzle and even distribution of material, with rapid solidification, when the material strikes a surface. Furthermore, as multiple layers are applied, they must flow together sufficiently to form a unitary structure, but not flow so much as to distort the shape of the structure. Lastly, the deposited structure should be relatively quickly hardened to a final form that is free of voids.
Typical slurry systems known in the art rely on photopolymerizable, thermoplastic, acrylate, or epoxy additives that cause the slurry to transform into a rigid mass after the slurry has been dispensed from an orifice. These additives comprise from 40 to 70% of the volume of the deposited slurry, resulting in either a significant change in volume or significant voids in the structure after the additives are removed prior to sintering. Furthermore, to prevent cracking, these non-volatile organic additives must be removed very slowly. This process typically involves heating the samples carefully for several days to burn off the additives.